This invention relates generally to transdermal drug delivery systems, and more particularly, to a transdermal drug delivery composition wherein a blend of polymers is utilized to affect the rate of drug delivery from the composition. More specifically, a plurality of polymers including a soluble polyvinylpyrrolidone having differing solubility parameters, preferably immiscible with each other, adjusts the solubility of the drug in a polymeric adhesive system formed by the blend, affects the maximum concentration of the drug in the system, and modulates the delivery of the drug from the composition and through the dermis.
The use of a transdermal composition, for example a pressure-sensitive adhesive containing a medicament, namely, a drug, as a means of controlling drug delivery through the skin at essentially a constant rate, is well known. Such known delivery systems involve incorporation of a medicament into a carrier such as a polymeric matrix and/or a pressure-sensitive adhesive formulation. The pressure-sensitive adhesive must adhere effectively to the skin and permit migration of the medicament from the carrier through the skin and into the bloodstream of the patient.
Drug concentration in a monolithic transdermal delivery system can vary widely depending on the drug and polymers used. For example, certain drugs are effective in low doses and therefore the transdermal formulation may involve low concentrations, illustratively 5% or less by weight of the medicament in an adhesive. Other drugs, such as nitroglycerin, require large doses to be effective and the transdermal formulation therefore may involve high drug concentrations, approximately between 5 to 40% or more by weight in an adhesive. Low concentrations of medicament typically do not critically affect the adhesion, tack, and shear resistance properties of the adhesive. However, low drug concentrations in the adhesive can result in difficulties in achieving an acceptable delivery rate of the medicament. High concentrations, on the other hand, frequently affect the adhesion properties of the adhesives. The deleterious effects are particularly exacerbated by drugs which also act as plasticizers or solvents for the polymeric adhesive (e.g., nitroglycerin in polyacrylates).
There is a need in the art for an adhesive composition for transdermal drug delivery systems which can selectably incorporate low concentrations of drug and deliver same at an adequate and controlled rate or incorporate high concentrations of drugs while retaining good physical adhesive properties.
In transdermal drug delivery systems, the presence of crystals (drugs and/or additives) is generally undesirable. If the drug is present in crystalline form, it is not available for release from the system, and therefore not available for delivery. Moreover, although drug crystals can first dissolve and then release from the system, such a process is usually rate-limiting and tends to reduce delivery.
Crystal size and distribution thus become important parameters which must be controlled in order to control delivery. These parameters are, however, usually difficult to control. Failure to control crystal size and distribution can result in products whose appearance suggests that the manufacturing process by which they are produced is not under control. More importantly, the presence of large crystals, particularly in excessive amounts, can be detrimental to adhesive-type transdermals. Crystals on the surface of the adhesive system can result in loss of tack. Furthermore, surface crystals can come into direct contact with the skin, and could cause skin irritation.
There is a need in the art for an adhesive composition for transdermal delivery systems which can prevent or suppress crystallization of drugs therein.
It is, therefore, an object of this invention to provide a transdermal drug delivery system wherein the rate of drug delivery from the transdermal composition may be selectably modulated.
It is another object of this invention to provide a transdermal drug delivery system wherein the rate of drug delivery from the transdermal composition may be selectably modulated by adjusting the solubility and/or diffusivity of the drug in the multiple polymer adhesive system.
It is also an object of this invention to provide a transdermal drug delivery system wherein the multiple polymer adhesive system is simple to manufacture.
It is a further object of this invention to provide a transdermal drug delivery system wherein drug-loading of a multiple polymer adhesive system may be selectably varied without adverse effects on drug delivery rate and adhesive properties, such as adhesion, tack, and shear resistance.
It is additionally an object of this invention to provide a transdermal drug delivery system wherein a novel multiple polymer adhesive system is provided which has desirable physical properties.